DESCRIPTION: This is an amended application which is a continuation study on the relationship of pain perception and myocardial ischemia during exercise and psychological stressful challenge. The overall hypothesis to be tested states that opioid peptide responses to stress are responsible for decreasing pain perception and resulting in silent myocardial ischemia. The proposed four year study will assess 60 subjects with a positive history of coronary artery disease (CAD) and compare findings with 40 age, sex, race, and blood pressure-matched healthy individuals who do not have coronary artery disease. The study will have a randomized double-blind placebo-controlled crossover design. Each patient will be studied over a 28-day study period, with a testing period in the first and last week of this study period in which the patient will be receiving placebo treatment or treatment with naltrexone, (an opioid antagonist). Each of the CAD subjects will receive 48-hour ambulatory Holter monitoring to track ischemic episodes. All subjects will receive exercise and psychological stress testing, and thermal and forearm ischemic pain testing at the beginning and end of the study period. The pain assessments will be performed prior to and following the stressors.